Intramedullary nails (known also as intramedullary rods) are well known for use in orthopedic surgery for repairing fractures of large bones, particularly the humerus. Recent examples of such intramedullary nails are disclosed in Perry U.S. Des. Pat. No. 379,855, Perry U.S. Pat. No. 5,766,174, and Itouran et al. U.S. Pat. No. 5,697,930, among others. Other humeral nails or rods (for the humerus) are commercially available for clinical use, such as the Ultramodular Trauma System of Howmedica, the modular nail of Richards Company, the Uniflex Humeral Nail of Biomet, and the Polarus Humeral Nail of Acumed.
Humeral nails or rods are used to repair the breakage of a large or long bone such as the humerus by advancing the nail axially through the hollow interior of the bone so that the nail cross the fracture site. Then, screws are applied to the nail through transverse apertures in the nail, extending through the bone on both sides of the site so that the nail is attached to portions of the bone on each side of the fracture, thus securing the bone into a single, immoveable piece once again and allowing healing to take place along the fracture site.
The various designs of intramedullary nail, and specifically humeral nails, which are available and known have certain disadvantages. For example, there is the danger that a humeral nail can have an oversized tip, so that when it is forcefully, longitudinally advanced into the bone interior, the oversized tip can be too large for the size of the bone medulla and split the bone, which can happen without warning. This of course, is a clinical disaster, greatly increasing the severity of the bone injury. With many prior art humeral nails, the problem is difficult to avoid, since the transverse dimensions of the medulla or marrow portion of the bone vary widely from patient to patient.
Also, problems can arise because the transverse bone screws which pass through the humeral nail can be insufficiently solidly retained to the humeral nail, causing the possibility of a small amount of "play" in the system, which of course transfers to the bone. However, if set screws are used in the bore of a tubular humeral nail for transverse screw retention, then it is not possible to use a guidewire system, as is highly desirable in many circumstances to aid in the emplacement of the humeral nail, because when the guidewire passes through the bore of such a humeral nail, the set screw of course interferes with the passage of the guidewire. Thus, although the use of set screws might be desirable to help to stabilize the bond between the emplaced humeral nail and transverse bone screws, this cannot be easily used with a guidewire system.
By this invention, an intramedullary nail (or rod) is provided, and specifically a humeral nail, which can be firmly secured to the transverse bone screws used with such a nail on a reliable basis. Also, the tip of the intramedullary nail of this invention is capable of entering into firm engagement with hard portions of the bone from a location within the medulla of the bone where the marrow resides, without providing so much pressure on the bone that there is a significant risk of fracture due to the outward pressure exerted by the emplaced nail.